Method for use of the synthesis gas that comes from a gasifier

ABSTRACT

A synthesis gas (H 2 +CO) that comes from a gasifier is supposed to be used in more efficient and optimal manner, particularly for generating electricity, whereby then, CO 2  that occurs at the same time is supposed to be passed to storage. This is achieved in that—the synthesis gas (H 2 +CO) and oxygen (O 2 ) from an air separation system are combusted in a burner, and relaxed by way of a gas turbine (driving a generator),—CO 2  is separated in the waste gas stream and passed to a compressor driven by the gas turbine, and—passed to CO 2  storage as compressed CO 2 .

The invention is directed at a method for use of the synthesis gas(H₂+CO) that comes from a gasifier (H₂+CO).

CO₂ necessarily occurs in the use of fossil fuels. In order not to haveto give this off into the atmosphere in the case of such combustionprocesses, efforts are made to capture and store the CO₂.

In a publication by the company RWE AG, “IGCC-CCS-Kraftwerk” [IGCC-CCSpower plant], a capture possibility on a large technical scale isdescribed, whereby “IGCC” means Integrated Gasification Combined Cycle(combined power plant with integrated coal gasification). Theabbreviation “CCS” means Carbon Capture and Storage.

In the method described, the gasification of coal is combined with CO₂capture, and current is generated in a downstream gas and steam turbine.In this connection, the coal is first converted into a combustible crudegas having the main components CO and H₂, in a gasifier, at hightemperatures, under pressure of approximately 35 bar. The gas ispurified, and the carbon monoxide is converted to CO₂ and H₂O, in a COshift reaction, with the aid of steam. After desulfurization, the CO₂ iscaptured, compressed, and passed to storage, whereby the remaininghydrogen is combusted in a gas turbine that drives a generator forgenerating electricity.

The starting point of the present invention is also fuel gasificationfor the production of synthesis gas, whereby here, any kind ofgasification is included. Such a synthesis gas should then be used inefficient and optimal manner, particularly for generating electricity,whereby the CO₂ that occurs at the same time is supposed to be passed tostorage.

This task is accomplished, according to the invention, with a method ofthe type mentioned initially, in that

-   -   the synthesis gas (H₂+CO) and oxygen (O₂) from an air separation        system are combusted in a burner, and relaxed by way of a gas        turbine (driving a generator),    -   CO₂ is separated in the waste gas stream and passed to a        compressor driven by the gas turbine, and    -   passed to CO₂ storage as compressed CO₂.

The invention makes use, in simple manner, of direct one-stage ortwo-stage compression of the CO₂ gas stream to pressures that allowstorage of the CO₂, if necessary after further compression.

In U.S. Pat. No. 5,724,805, a method is known in which liquid CO₂ iscollected in a tank, among other things. In this connection, tapping ofthe CO₂ passed to sequestration takes place on the pressure-free side ofthe gas turbine, after the waste heat steam generator. Therefore thefull compression power for the sequestration must be generatedseparately, while in the case of the present invention, pre-compressionby the compressor of the gas turbine itself takes place, as indicatedabove. Here, the full compression power is therefore utilized by the gasturbine. Liquefaction of the CO₂ does not take place.

Embodiments of the invention are evident from the dependent claims. Inthis connection, it can be provided that part of the compressed CO₂ gasis passed to the burner, for temperature control.

Feed of the compressed CO₂ gas into streams that lead to the burner cantake place at different positions. Either directly into the synthesisgas stream that is fed to the burner, or also into the oxygen streamfrom the air separation system that is fed to the burner.

Further optimization of the method of operation according to theinvention consists in that heat for operation of a steam turbine istaken from the waste gas stream from the gas turbine, by way of a heatexchanger, whereby the steam turbine can be used to drive a generator.

A further embodiment consists in that the stream that leaves the gasturbine is subjected to separation of CO₂ and steam, in such a mannerthat pure CO₂ is applied to the compressor coupled with the gas turbine.

Further characteristics, details, and advantages of the invention areevident from the example described below, using the fundamentalschematic of a system according to the invention.

A fuel generally indicated with 1, along with additives 2, is passed togrinding and drying and a pressurized space, as indicated with 3. Thefuel can be slurry, hard coal or soft coal, biomass, petcoke, oil sand,Orimulsion, treated garbage, and the like. This fuel is then applied toa gasification system 4, together with oxygen (line 5) from an airseparation system 6, whereby nitrogen, for example, is applied to theregion of grinding, drying, and compacting 3, by way of the line 7.

The crude gas that comes from the gasification system 4 is firstintroduced into the quench 5 that serves to remove dust from the gas.Here, not only the dust but, at the same time, the ammonia that ispresent in the gas and the hydrogen cyanide, as well as the hydrogensulfide, are washed out almost completely. This product is then appliedto the subsequent CO₂ conversion, whereby this step serves to increasethe synthesis gas temperature and to react COS to H₂S and HCN to NH₃ andCO. High-temperature conversion and medium-temperature andlow-temperature conversion are known, for example, whereby other methodscan also be used. In the example shown, the conversion 6 is followed byhydrolysis 7 for removal of carbonyl sulfide. Here, the carbonyl sulfidethat is present in the gas, and is very difficult to wash out with waterand other usual solvents, is converted to hydrogen sulfide by means ofcatalytic hydrolysis, whereby the carbonyl sulfide reacts with steam, inthe gas phase, according to the reaction equation COS+H₂O→H₂S+CO₂.

Finally, H₂S scrubbing 8 still follows, whereby here, the hydrogensulfide present in the gas is adsorptively washed out with a scrubbingsolution that acts selectively. In this connection, it should be notedthat other possibilities for H₂S removal are also possible, such ashigh-temperature dry desulfurization, for example.

After these treatment steps, the gas has sufficient purity so that itcan be passed to the combustion chamber, indicated with 9, of a gasturbine 10.

As is evident from the fundamental schematic, oxygen that comes from theair separation system 6 is also applied to the combustion chamber 9, byway of the line 11.

Not only a generator 12 that produces electricity, but also a gascompressor 13 is coupled with the gas turbine 10; this compressorcompresses the gas that leaves the gas turbine according to line 14,whereby according to the invention, this is a CO₂ compressor. The wastegas that leaves the gas turbine 10 is passed to steam generation by wayof a heat exchanger 15, whereby the steam that is formed is passed toanother gas turbine 16 having a generator 17 for producing electricity.

After the heat exchanger 15, the gas stream 14 is subsequently passed byway of a CO₂/steam separation device, indicated in general with 18. TheCO₂ that leaves the CO₂ compressor 13 is then passed to CO₂ storage, byway of the line 19, as indicated with the line 20.

As is also shown in the figure, the CO₂ gas that leaves the CO₂compressor 13 can particularly also be passed into the burner chamber 9to regulate its temperature, either according to arrow 21, to thesynthesis gas stream, or by way of the line 22, to the O₂ stream 11 thatcomes from the air separation system.

Of course, the example described can still be modified in many respectswithout departing from the basic idea. For example, as has already beenindicated above, any type of gasifier can be used here; in the area ofCO conversion, a gas/gas heat exchanger can also be provided, ifnecessary, in order to achieve the temperature for hydrolysis, and moreof the like.

1. Method for use of a synthesis gas (H₂+CO) that comes from a gasifier,wherein the synthesis gas (H₂+CO) and oxygen (O₂) from an air separationsystem are combusted in a burner, and relaxed by way of a gas turbine(driving a generator), CO₂ is separated in the waste gas stream andpassed to a compressor driven by the gas turbine, and passed to CO₂storage as compressed CO₂.
 2. Method according to claim 1, wherein partof the compressed CO₂ gas is passed to the burner for temperaturecontrol.
 3. Method according to claim 2, wherein the part of thecompressed CO₂ gas is passed to the synthesis gas stream or to the O₂stream from the air separation system ahead of the burner.
 4. Methodaccording to claim 1, wherein heat for operation of a steam turbine(with generator) is taken from the waste gas stream from the gasturbine, by way of a heat exchanger.